This invention relates to railway vehicles.
For present purposes railway vehicles may be typified as being of two kinds. In the first kind the body of the vehicle is directly supported on wheelsets each of which has a pair of wheels firmly mounted on the axle. In the other kind the body is pivotally supported on bogies which in turn are directly supported on wheelsets.
In this specification and in the appended claims the term "railway truck" is defined to mean a railway unit including a frame supported on a plurality of wheelsets. Thus a railway truck may be a bogie or a vehicle, the frame being the body in the case of a vehicle and being the bogie frame in the case of a bogie.
Self-steering or radial railway trucks are known--see e.g. U.S. Pat. Nos. 4,067,261 and 4,067,262--and many such trucks are in use on the South African railway system and elsewhere in the world. Such trucks rely on wheeltreads with a high effective conicity and a spring suspension which is soft in yaw thus allowing the wheeltreads to effect self-steering.
In U.S. Pat. No. 4,067,261 the resilient elements 24 are sufficiently soft to permit the yawing motion of the wheelset relative to the truck frame or vehicle body but would deflect excessively if subjected to longitudinal forces developed between the wheelset and the truck frame. FIGS. 3 and 4 of U.S. Pat. No. 4,067,261 provide for longitudinal members 38 and 50 respectively which couple the centre of the wheelset to the truck frame. Traction forces could be transmitted through these members without restraining the axle in yaw. The two arrangments depicted by FIGS. 3 and 4 require the expense of the placing of a bearing at the centre of yaw of the wheelset, and the use of space normally occupied by traction equipment in a motorized bogie. Furthermore the longitudinal members are not suitable for taking compressive loads because, if the direction of these loads does not coincide with the longitudinal axis of the members, forces normal to this axis will tend to cause the mechanism to collapse. In addition relative vertical and lateral motion between the wheelset and the truck frame results in a change in the wheelbase causing dynamic interference.
In U.S. Pat. No. 4,480,553 it has been proposed to add along the sides of the truck a set of interconnections which, together with cross-anchors, inhibit the wheelsets from moving longitudinally relative to the truck frame. These interconnections may be oriented to permit free relative motion between the wheelsets and the truck frame in either the vertical or lateral planes. If, for example, the orientation is chosen to permit free lateral motion the interconnections will cause a change in wheelbase due to vertical motion between the wheelsets and the truck frame resulting in dynamic interference. Because of this limitation practical applications of U.S. Pat. No. 4,480,553 have been restricted to trucks having primary axlebox suspensions which are relatively stiff in the vertical plane.
U.S. Pat. No. 4,067,261 makes provision for an axlebox suspension which allows for vertical deflection at the axlebox and hence for the application of the self-steering principle to rigid frame trucks which by necessity require a primary suspension. FIG. 14 illustrates such an application but has never been utilized because of the complexity and difficulty in designing and predicting the wheelset yaw stiffness achieved in practice with such a mechanism.
It would be an advantage to provide a mechanism which has means connecting the axleboxes of the wheelsets to the truck frame in a manner which inhibits longitudinal movement of the centre of yaw of each wheelset in relation to the frame but allows vertical and lateral movement of the wheelsets relative to the frame and also allows the wheelsets to yaw thus permitting the self-steering or radial action of the wheelsets on curved track. The mechanism should permit the stiffness of the axle in yaw to be practicably obtainable under railway design conditions. Space should be available for conventional traction equipment when required.